Lead monitoring frequency based on lead and patient characteristics

ABSTRACT

A method and device for updating a frequency of determining whether a lead condition is occurring in a medical device that includes sensing a cardiac signal, determining whether a lead condition is occurring in response to the sensed cardiac signal, determining whether a first patient characteristic is satisfied during a plurality of predetermined update periods, performing a first update of a virtual lead days value associated with a number of days since implant of the lead in response to the first patient characteristic being satisfied, determining whether a patient characteristic update is satisfied in response to a second patient characteristic, different than the first patient characteristic, being satisfied, performing a second update of the virtual lead days value in response to the patient characteristic update being satisfied, and updating a frequency of determining whether the lead condition is occurring in response to the updated virtual lead days value.

RELATED APPLICATION

Cross-reference is hereby made to commonly assigned U.S. patentapplication Ser. No. ______, filed on even date herewith (Attorneydocket number C00005467.USU1) entitled “LEAD MONITORING FREQUENCY BASEDON LEAD AND PATIENT CHARACTERISTICS” and U.S. patent application Ser.No. ______, filed on even date herewith (Attorney docket numberC00005467.USU3) entitled “LEAD MONITORING FREQUENCY BASED ON LEAD ANDPATIENT CHARACTERISTICS”, and incorporated by reference in it'sentirety.

FIELD OF THE DISCLOSURE

The disclosure relates generally to medical devices configured fordelivering electrical therapies to a patient, and in particular, thedisclosure relates to a method and device for monitoring changes in leadintegrity in a medical device.

BACKGROUND

A variety of medical devices for delivering a therapy and/or monitoringa physiological condition have been used clinically or proposed forclinical use in patients. Examples include medical devices that delivertherapy to and/or monitor conditions associated with the heart, muscle,nerve, brain, stomach or other organs or tissues. Some therapies includethe delivery of electrical signals, e.g., stimulation, to such organs ortissues. Some medical devices may employ one or more elongatedelectrical leads having electrodes positioned thereon for deliveringand/or receiving signals. For example, electrodes may be included foruse in one or both of the delivery of therapeutic electrical signals tosuch organs or tissues, and the sensing of intrinsic electrical signalswithin the patient, which may be generated by such organs or tissue. Inaddition, the elongated lead may include other sensors positionedthereon for sensing physiological parameters of a patient.

Medical leads may be configured to allow the electrodes or other sensorsto be positioned at desired locations for delivery of therapeuticelectrical signals or sensing. For example, the electrodes or sensorsmay be carried at a distal portion of a lead. A proximal portion of thelead may be coupled to a medical device housing, which may containcircuitry such as signal generation and/or sensing circuitry. In somecases, the medical leads and the medical device housing are implantablewithin the patient. Medical devices with a housing configured forimplantation within the patient may be referred to as implantablemedical devices.

Implantable cardiac pacemakers or cardioverter-defibrillators, forexample, provide therapeutic electrical signals to the heart viaelectrodes carried by one or more implantable medical leads. Thetherapeutic electrical signals may include pulses or shocks for pacing,cardioversion, or defibrillation. In some cases, a medical device maysense intrinsic depolarizations of the heart, and control delivery oftherapeutic signals to the heart based on the sensed depolarizations.Upon detection of an abnormal rhythm, such as bradycardia, tachycardiaor fibrillation, an appropriate therapeutic electrical signal or signalsmay be delivered to restore or maintain a more normal rhythm. Forexample, in some cases, an implantable medical device may deliver pacingstimulation to the heart of the patient upon detecting tachycardia orbradycardia, and deliver cardioversion or defibrillation shocks to theheart upon detecting fibrillation.

Implantable medical leads typically include a lead body containing oneor more elongated electrical conductors that extend through the leadbody from a connector assembly provided at a proximal lead end to one ormore electrodes located at the distal lead end or elsewhere along thelength of the lead body. The conductors connect signal generation and/orsensing circuitry within an associated implantable medical devicehousing to respective electrodes or sensors. Some electrodes may be usedfor both delivery of therapeutic signals and sensing. Each electricalconductor is typically electrically isolated from other electricalconductors and is encased within an outer sheath that electricallyinsulates the lead conductors from body tissue and fluids.

Medical lead bodies implanted for cardiac applications tend to becontinuously flexed by the beating of the heart. Other stresses may beapplied to the lead body, including the conductors therein, duringimplantation or lead repositioning. Patient movement can cause the routetraversed by the lead body to be constricted or otherwise altered,causing stresses on the lead body and conductors. In rare instances,such stresses may fracture a conductor within the lead body. Thefracture may be continuously present, or may intermittently manifest asthe lead flexes and moves during normal day to day patient activityand/or contraction of a beating heart.

Additionally, the electrical connection between medical device connectorelements and the lead connector elements can be intermittently orcontinuously disrupted. For example, connection mechanisms, such as setscrews, may be insufficiently tightened at the time of implantation,followed by a gradual loosening of the connection. Also, lead pins maynot be completely inserted.

Lead fracture, disrupted connections, or other causes of short circuitsor open circuits may be referred to, in general, as lead integrityconditions. In the case of cardiac leads, sensing of an intrinsic heartrhythm through a lead can be altered by lead integrity conditions.Identifying lead integrity conditions may be challenging, particularlyin a clinic, hospital or operating room setting, due to the oftenintermittent nature of lead integrity conditions.

When these lead problems manifest themselves, it is necessary for theclinician to diagnose the nature of the lead related condition from theavailable data, IMD test routines, and patient symptoms. Once diagnosed,the clinician must take corrective action, for example, re-program tounipolar polarity, open the pocket to replace the lead, reposition theelectrodes or sensors, or tighten the proximal connection.

Lead impedance data and other parameter data, for example, withoutlimitation, electrogram (EGM), battery voltage, switching from bipolarto unipolar configuration, error counts, and LOC/LOS data, may becompiled and displayed on a programmer screen and/or printed out foranalysis by the clinician. The clinician may also undertake real timeIMD parameter reprogramming and testing while observing the monitoredsurface ECG to try to pinpoint a suspected lead related condition thatis indicated by the data and/or patient and/or device symptoms.

Several approaches have been suggested to provide physicians withinformation and/or early detection or prevention of these lead-relatedconditions. Commonly assigned U.S. Pat. No. 5,861,012 (Stroebel),incorporated herein by reference, describes several approaches toautomatically determine the pacing threshold. Periodically, a pacingthreshold test is conducted wherein the pacing pulse width and amplitudeare reduced to determine chronaxie and rheobase values to capture theheart. These threshold test data are stored in memory, and used tocalculate a “safety margin” to ensure capture.

Certain external programmers that address the analysis of such data andsymptoms include those disclosed in the following U.S. Pat. No.4,825,869 (Sasmor et al.); U.S. Pat. No. 5,660,183 (Chiang et al.); andU.S. Pat. No. 5,891,179 (ER et al.), all incorporated herein byreference. The '869 patent describes processing a variety of uplinked,telemetered atrial and ventricular EGM data, stored parameter and eventdata, and the surface ECG in rule-based algorithms for determiningvarious IPG and lead malfunctions. The '183 patent also considerspatient symptoms in an interactive probability based expert system thatcompares data and patient systems to stored diagnostic rules, relatingsymptoms to etiologies so as to develop a prognosis. The '179 patentdiscloses a programmer that can be operated to provide a kind oftime-varying display of lead impedance values in relation to upper andlower impedance limits. The lead impedance values are derived frompacing output pulse current and voltage values. These values are theneither measured and stored in the IPG memory from an earlier time orrepresent current, real-time values that are telemetered to theprogrammer for processing and display.

Prior art detection of lead-related conditions and various IPG responsesto such detection are set forth in the following U.S. Pat. No. 4,140,131(Dutcher et al.); U.S. Pat. No. 4,549,548 (Wittkampf et al.); U.S. Pat.No. 4,606,349 (Livingston et al.); U.S. Pat. No. 4,899,750 (Ekwall);U.S. Pat. No. 5,003,975 (Hafelfinger et al.); U.S. Pat. No. 5,137,021(Wayne et al.); U.S. Pat. No. 5,156,149 (Hudrlik); U.S. Pat. No.5,184,614 (Collins); U.S. Pat. No. 5,201,808 (Steinhaus et al.); U.S.Pat. No. 5,201,865 (Kuehn); U.S. Pat. No. 5,224,475 (Berg et al.); U.S.Pat. No. 5,344,430 (Berg et al.); U.S. Pat. No. 5,350,410 (Kieks etal.); U.S. Pat. No. 5,431,692 (Hansen et al.); U.S. Pat. No. 5,453,468(Williams et al.); U.S. Pat. No. 5,507,786 (Morgan et al.); U.S. Pat.No. 5,534,018 (Walhstrand et al.); U.S. Pat. No. 5,549,646 (Katz etal.); U.S. Pat. No. 5,722,997 (Nedungadi et al.); U.S. Pat. No.5,741,311 (McVenes et al.); U.S. Pat. No. 5,755,742 (Schuelke et al.);and U.S. Pat. No. 5,814,088 (Paul et al.). All of these patents areincorporated herein by reference.

Because implanted leads can be critical to providing life sustainingtherapy and may fail at various rates, identification of lead integrityconditions may allow modifications of the therapy or sensing, or leadreplacement. Ideal lead monitoring would include continuous monitoringof lead characteristics using related characteristics, such as impedanceand electrogram signals of the lead. However, such continuous monitoringis not possible given the limited resources within the implantablemedical device. While the occurrence of lead integrity issues tends tobe rare, many factors may contribute to lead failure. For example, theage of the patient may be contribute to the occurrence of issues leadingto failure, with an increase in the number of lead integrity issuesoccurring for younger patients. Other factors may include the gender ofthe patient, the level of activity of the patient, or how long thedevice has been implanted in the patient, etc. Therefore, what is neededis a method and apparatus for varying lead monitoring when needed basedon multiple factors associated with increased failure risk.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of an implantable medical device(IMD) capable of delivering high voltage and low voltage therapies to aheart.

FIG. 2 is a functional block diagram of the IMD shown in FIG. 1according to an illustrative embodiment.

FIG. 3 is a flowchart of an exemplary method of determining leadintegrity monitoring frequency in a medical device according to anembodiment of the disclosure.

FIG. 4 is a timeline illustrating updating of the frequency of leadintegrity monitoring according to an embodiment of the presentdisclosure.

FIG. 5 is a flowchart of an exemplary method of determining leadintegrity monitoring frequency in a medical device according to anembodiment of the disclosure.

FIG. 6 is a flowchart of an exemplary method of determining leadintegrity monitoring frequency in a medical device according to anembodiment of the disclosure.

FIG. 7 is a flowchart of an exemplary method of determining leadintegrity monitoring frequency in a medical device according to anembodiment of the disclosure.

FIG. 8 is a flowchart of an exemplary method of determining leadintegrity monitoring frequency in a medical device according to anembodiment of the disclosure.

FIG. 9 is a flowchart of an exemplary method of determining leadintegrity monitoring frequency in a medical device according to anembodiment of the disclosure.

FIG. 10 is a flowchart of an exemplary method of determining leadintegrity monitoring frequency in a medical device according to anembodiment of the disclosure.

DETAILED DESCRIPTION

In the following description, references are made to illustrativeembodiments. It is understood that other embodiments may be utilizedwithout departing from the scope of the disclosure. As used herein, theterm “module” refers to an application specific integrated circuit(ASIC), an electronic circuit, a processor (shared, dedicated, or group)and memory that execute one or more software or firmware programs, acombinational logic circuit, or other suitable components that providethe described functionality.

FIG. 1 is a schematic representation of an implantable medical device(IMD) 10 capable of delivering high voltage and low voltage therapies toheart 12. IMD 10 is coupled to heart 12 via leads 14, 16 and 18. Rightatrial lead 14 extends from IMD 10 to the right atrium (RA) and carriesdistal electrodes 20 and 22 for sensing cardiac electrical signals anddelivering pacing pulses in the RA.

Right ventricular lead 16 carries a tip electrode 30 and a ringelectrode 32 for sensing cardiac electrical signals and deliveringpacing pulses in the RV. RV lead 16 additionally carries high voltagecoil electrodes 34 and 36, referred to herein as the RV coil electrode34 and the superior vena cava (SVC) coil electrode 36, for deliveringhigh voltage cardioversion and defibrillation shocks in response todetecting a shockable tachyarrhythmia from sensed cardiac signals. Inaddition, a housing electrode 26, also referred to as a CAN electrode,can be formed as part of the outer surface of the housing of IMD 10 andbe used as an active electrode in combination with coil electrodes 34and/or 36 during shock delivery.

A coronary sinus (CS) lead 18 is shown extending into a cardiac vein 50via the RA and coronary sinus for positioning electrodes 40 and 42 forsensing cardiac signals and delivering pacing pulses along the leftventricle. In some examples, CS lead 18 may additionally carryelectrodes for positioning along the left atrium for sensing andstimulation along the left atrial chamber.

The depicted positions in or about the right and left heart chambers aremerely illustrative. Other leads and pace/sense electrodes and/or highvoltage electrodes can be used instead of, or in combination with, anyone or more of the depicted leads and electrodes shown in FIG. 1. Leadand electrode configurations are not limited to transvenous leads andintravenous or intracardiac electrodes as shown in FIG. 1. In someembodiments, an IMD system may include subcutaneous electrodes, whichmay be carried by an extravenous lead extending from IMD 10 or leadlesselectrodes incorporated along the IMD housing.

IMD 10 is shown as a multi-chamber device capable of sensing andstimulation in three or all four heart chambers. It is understood thatIMD 10 may be modified to operate as a single chamber device, e.g. witha lead positioned in the RV only, or a dual chamber device, e.g. with alead positioned in the RA and a lead positioned in the RV. In general,IMD 10 may be embodied as any single, dual or multi-chamber deviceincluding lead and electrode systems for delivering at least a highvoltage therapy and may be configured for delivering both high voltageshock pulses and low voltage pacing pulses.

FIG. 2 is a functional block diagram of the IMD 10 shown in FIG. 1according to an illustrative embodiment. IMD 10 includes a sensingmodule 102, a therapy delivery module 104, a telemetry module 106,memory 108, and a control unit 112, also referred to herein as“controller” 112.

Sensing module 102 is coupled to electrodes 20, 22, 30, 32, 34, 36, 40,42 and housing electrode 26 (all shown in FIG. 1) for sensing cardiacelectrogram (EGM) signals. Sensing module 102 monitors cardiacelectrical signals for sensing signals attendant to the depolarizationof myocardial tissue, e.g. P-waves and R-waves, from selected ones ofelectrodes 20, 22, 26, 30, 32, 34, 36, 40, and 42 in order to monitorelectrical activity of heart 12. Sensing module 102 may include a switchmodule to select which of the available electrodes are used to sense thecardiac electrical activity. The switch module may include a switcharray, switch matrix, multiplexer, or any other type of switching devicesuitable to selectively couple electrodes to sensing module 102. In someexamples, controller 112 selects the electrodes to function as senseelectrodes, or the sensing vector, via the switch module within sensingmodule 102.

Sensing module 102 may include multiple sensing channels, each of whichmay be selectively coupled to respective combinations of electrodes 20,22, 26, 30, 32, 34, 36, 40, and 42 to detect electrical activity of aparticular chamber of heart 12, e.g. an atrial sensing channel and aventricular sensing channel. Different sensing channels may additionallyor alternatively be coupled to various electrode combinations forproviding both near field (NF) sensing vectors and far field (FF)sensing vectors. For example, a NF sensing vector may be sensed betweenRV tip electrode 30 and RV ring electrode 32. A FF sensing vector may besensed between RV coil electrode 34 and SVC coil electrode 36. Eachsensing channel may comprise an amplifier that outputs an indication tocontroller 112 in response to sensing of a cardiac depolarization, inthe respective chamber of heart 12. In this manner, controller 112 mayreceive sense event signals corresponding to the occurrence of R-wavesand P-waves in the various chambers of heart 12. Sensing module 102 mayfurther include digital signal processing circuitry for providingcontroller 112 with digitized EGM signals, which may be used todetermine EGM signal features or for signal morphology analysis in someembodiments.

Sensing module 102 and control unit 112 are configured to monitor thepatient's cardiac rhythm for determining a need for therapy delivery andfor timing therapy delivery. In response to detecting a tachyarrhythmia,controller 112 controls therapy delivery module 104 to deliver a therapyaccording to programmed therapies stored in memory 108.

Sensing module 102 may include impedance monitoring circuitry 105 formeasuring current between a measurement pair of electrodes 20 through 42in response to a drive signal. The drive signal is generally a lowvoltage signal, and impedance measurements may be used by control 112 todetect short circuit conditions or other lead-related issues detectablewhen a low voltage drive signal is used. Such low voltage impedancemeasurements may be performed periodically or in response to loss ofpacing capture or a change in pacing threshold to detect lead-relatedissues. As will be described herein, impedance monitoring may becontrolled and adjusted to promote the identification of a short circuitcondition, as evidenced by a decrease in impedance.

Sensing module 102 provides control unit 112 digitized EGM signals fordetecting a possible insulation breach and short circuit condition insome embodiments. As further described below, control unit 112 includesprocessing circuitry for analyzing the EGM signal to detect a signaturenoise waveform that is characteristic of a short circuit condition. Inparticular, a high priority is given to monitoring for a short circuitcondition that could lead to shorting of a HV shock delivered to treat amalignant tachyarrhythmia. Real-time monitoring for a short circuitcondition is described herein. It is contemplated, however, thatidentification of a short circuit condition may be performed during postprocessing. An epoch of data (e.g. 10 sec) could be stored at regularintervals in the memory 108 or triggered storage based on a detectedevent. The data may be post-processed either within the IMD or anexternal device.

Therapy delivery module 104 is coupled to electrodes 20, 22, 26, 30, 32,34, 36, 40, and 42 for delivering electrical stimulation therapy to thepatient's heart. In some embodiments, therapy delivery module 104includes low voltage (LV) therapy circuitry 120 including a pulsegenerator for generating and delivering LV pacing pulses duringbradycardia pacing, cardiac resynchronization therapy (CRT), andanti-tachycardia pacing (ATP). Control unit 112 controls LV therapycircuitry 120 to deliver pacing pulses according to programmed controlparameters using electrodes pacing electrodes 20, 22, 30, 32, 40 and/or42 for example. Electrodes 20, 22, 30 32, 40 and 42 are generallyreferred to a “low voltage” electrodes because they are normally usedfor delivering relatively low voltage therapies such as pacing therapiesas compared to the high voltage therapies, i.e. cardioversion anddefibrillation therapies, delivered by high voltage coil electrodes 32and 34. However, as will be described herein, in some instances LVelectrodes 20, 22, 30, 32 40 and 42 may be used for delivering a highvoltage therapy in response to detection of a high voltage short circuitcondition.

Therapy delivery module 104 includes high voltage (HV) therapy deliverycircuitry 130 for generating and delivering high voltage cardioversionand defibrillation shock pulses. HV therapy delivery circuitry 130includes HV capacitors 132 that are charged in response to detecting ashockable cardiac rhythm, e.g. a ventricular tachycardia or ventricularfibrillation. After determining HV capacitors 132 have reached atargeted charge voltage, according to a programmed shock energy, HVtherapy delivery 130 delivers a shock pulse via selected HV electrodes,e.g. coil electrodes 34, 36 and housing electrode 26.

HV therapy circuitry 130 includes short circuit (SC) protectioncircuitry for protecting IMD 10 against a short circuit fault during HVtherapy delivery. In one embodiment, SC protection circuitry 134monitors the current during the shock pulse delivery and in response toa relatively high current, i.e. very low impedance, SC protectioncircuitry 134 immediately terminates the shock pulse, e.g. by anelectronic switch, to prevent damage to the circuitry of IMD 10. The HVshort circuit condition would prevent delivery of the HV shock to theheart and would fail to terminate a detected shockable rhythm. Byprotecting the IMD circuitry from the SC fault, controller 112 remainsoperable to alter the HV therapy delivery to still treat thetachyarrhythmia and/or control therapy delivery module 104 to deliveralternative electrical stimulation therapies.

In response to identifying a short circuit condition, controller 112 maystore in memory 108 an electrode vector and polarity combination beingused that provided evidence of a short circuit condition. Thisinformation may be retrieved and used by a clinician in resolving theshort circuit condition, e.g. by replacing a lead or reprogramming thetherapy delivery electrode configuration and polarity. This informationmay be used by controller 112 in selecting electrode vectors andpolarities for delivering future HV and/or LV therapies.

Therapy delivery module 104 includes HV switching circuitry 136 used forcontrolling the pathway through which HV capacitors 132 are discharged.HV switching circuitry 136 may include a switch array, switch matrix,multiplexer, or any other type of switching device suitable toselectively couple combinations of low voltage electrodes (e.g.electrodes 20, 22, 30, 32, 40 and 42) and/or high voltage electrodes(e.g. electrodes 34 and 36) and housing electrode 26 to HV therapycircuitry 130. In some examples, controller 112 selects a shock vectorusing any of HV coil electrodes 34, 36 and housing electrode 26. As willbe described below, controller 112 may select the polarity of theelectrodes included in the shock vector using switching circuitry 136.

In some embodiments, the HV capacitors may be coupled to multiple pacingelectrode cathodes simultaneously, e.g. any combination or all of LVelectrodes 20, 22, 30, 32, 40 and 42 for delivering a HV shock inresponse to a HV short circuit condition. The anode may be any of thecoil electrodes 34, 36, housing electrode 26 or combination of remainingLV electrodes 20, 22, 30, 32, 40 and 42 or any other housing based orlead based electrodes that may be available in the particular IMDsystem. Pacing capacitors coupled to electrodes 20, 22, 30, 32, 40 and42 included in LV therapy circuitry 120 may be used in distributing theHV charge remaining on the HV capacitor(s) 132 in some embodiments in anattempt to deliver a needed shock therapy. In this case the pacingcapacitors are rated for adequately high voltage to distribute the shockenergy among selected electrodes.

Controller 112 may be embodied as a processor including any one or moreof a microprocessor, a digital signal processor (DSP), an applicationspecific integrated circuit (ASIC), a field-programmable gate array(FPGA), or equivalent discrete or integrated logic circuitry. In someexamples, controller 112 may include multiple components, such as anycombination of one or more microprocessors, one or more controllers, oneor more DSPs, one or more ASICs, or one or more FPGAs, as well as otherdiscrete or integrated logic circuitry. The functions attributed tocontroller 112 herein may be embodied as software, firmware, hardware orany combination thereof. Controller 112 includes a therapy control unitthat controls therapy module 104 to deliver therapies to heart 12according to a selected one or more therapy programs, which may bestored in memory 108. Controller 112 and associated memory 108 arecoupled to the various components of IMD 10 via a data/address bus.

Memory 108 stores intervals, counters, or other data used by controller112 to control sensing module 102, therapy delivery module 104 andtelemetry module 106. Such data may include intervals and counters usedby controller 112 for detecting a heart rhythm and to control thedelivery of therapeutic pulses to heart 12. Memory 108 also storesintervals for controlling cardiac sensing functions such as blankingintervals and refractory sensing intervals. Events (P-waves and R-waves)sensed by sensing module 102 may be identified based on their occurrenceoutside a blanking interval and inside or outside of a refractorysensing interval.

Memory 108 may store computer-readable instructions that, when executedby controller 112, cause IMD 10 to perform various functions attributedthroughout this disclosure to IMD 10. The computer-readable instructionsmay be encoded within memory 108. Memory 108 may comprise non-transitorycomputer-readable storage media including any volatile, non-volatile,magnetic, optical, or electrical media, such as a random access memory(RAM), read-only memory (ROM), non-volatile RAM (NVRAM),electrically-erasable programmable ROM (EEPROM), flash memory, or anyother digital media, with the sole exception being a transitorypropagating signal.

Tachyarrhythmia detection algorithms may be stored in memory 108 andexecuted by controller 112 for detecting ventricular tachycardia (VT),ventricular fibrillation (VF) as well as discriminating such ventriculartachyarrhythmias, generally referred to herein as “shockable rhythms”from atrial or supraventricular tacharrhythmias, such as sinustachycardia and atrial fibrillation (A FIB). Ventricular event intervals(R-R intervals) sensed from the EGM signals are commonly used fordetecting cardiac rhythms. Additional information obtained such asR-wave morphology, slew rate, other event intervals (e.g., P-P intervalsand P-R intervals) or other sensor signal information may be used indetecting, confirming or discriminating an arrhythmia. Reference is madeto U.S. Pat. No. 5,354,316 (Keimel), U.S. Pat. No. 5,545,186 (Olson etal.) and U.S. Pat. No. 6,393,316 (Gillberg et al.) for examples ofarrhythmia detection and discrimination using EGM signals, all of whichpatents are incorporated herein by reference in their entirety. Thetechniques described herein for detecting a short circuit condition andresponding thereto may be implemented in the types of devices disclosedin the above-referenced patents.

In response to detecting a shockable rhythm, a programmed therapy isdelivered by therapy delivery module 104 under the control of controller112. A description of high-voltage output circuitry and control ofhigh-voltage shock pulse delivery is provided in the above-incorporated'186 Olson patent. Typically, a tiered menu of arrhythmia therapies areprogrammed into the device ahead of time by the physician and stored inmemory 108. For example, on initial detection of a ventriculartachycardia, an anti-tachycardia pacing therapy may be selected anddelivered. On redetection of the ventricular tachycardia, a moreaggressive anti-tachycardia pacing therapy may be scheduled. If repeatedattempts at anti-tachycardia pacing therapies fail, a HV cardioversionpulse may be selected thereafter. Therapies for tachycardia terminationmay also vary with the rate of the detected tachycardia, with thetherapies increasing in aggressiveness as the rate of the detectedtachycardia increases. For example, fewer attempts at anti-tachycardiapacing may be undertaken prior to delivery of cardioversion pulses ifthe rate of the detected tachycardia is above a preset threshold.

In the event that ventricular fibrillation is identified, high frequencyburst stimulation may be employed as the initial attempted therapy.Subsequent therapies may be delivery of HV defibrillation shock pulses,typically in excess of 5 Joules, and more typically in the range of 20to 35 Joules. Lower energy levels may be employed for cardioversion. Inthe absence of a HV short circuit condition, the defibrillation pulseenergy may be increased in response to failure of an initial pulse orpulses to terminate fibrillation.

IMD 10 may additionally be coupled to one or more physiological sensors.Physiological sensors may include pressure sensors, accelerometers, flowsensors, blood chemistry sensors, activity sensors or otherphysiological sensors known for use with implantable cardiac stimulationdevices. Physiological sensors may be carried by leads extending fromIMD 10 or incorporated in or on the IMD housing. Sensor signals may beused in conjunction with EGM signals for detecting and/or confirming aheart rhythm. An activity sensor 109 may be optionally included in someexamples of IMD 10. Activity sensor 109 may include one or moreaccelerometers. Activity sensor 109 may additionally or alternativelyinclude other sensors such as a heart sounds sensor, a pressure sensor,or an oxygen saturation sensor. Activity sensor 109 may detectrespiration via one or more electrodes. Information obtained fromactivity sensor 109 may be used to determine activity level, posture,blood oxygen level or respiratory rate, for example, leading up to, orat the time of the abnormal heart rhythm. In some examples, thisinformation from activity sensor 109 may be used by IMD 10 to aid in thedetermination as to whether to update the lead integrity monitoringfrequency, as described below in detail.

Telemetry module 106 is used for transmitting data accumulated by IMD 10wirelessly to an external device 150, such as a programmer, homemonitor, or handheld appliance. Examples of communication techniquesused by IMD 10 include low frequency or radiofrequency (RF) telemetry,which may be an RF link established via Bluetooth, WiFi, or MICS. IMD 10may receive programming commands and algorithms from external device 150via telemetry link 152 with telemetry module 106. For example, externaldevice 150 may be used to program SC detection parameters used bycontroller 112. Telemetry module 106 may be controlled by controller 112for delivering a patient or clinician alert or notification to externaldevice 150 in response to detecting a short circuit condition.

IMD 10 may optionally be equipped with alarm circuitry 110 for notifyingthe patient or other responder that a patient alert condition has beendetected by IMD 10. In one embodiment, the alarm 110 may emit an audibletone or notification to alert the patient or a responder that immediatemedical attention is required. For example, when a short circuitcondition is detected, particularly a short circuit involving HV coilelectrodes 34 and 36, alarm 110 may be used to notify the patient, acaregiver or other responder that medical attention is required. In someembodiments, alarm 110 calls an emergency number directly via a wirelesscommunication network.

FIG. 3 is a flowchart of an exemplary method of determining leadintegrity monitoring frequency in a medical device according to anembodiment of the disclosure. During implant of the device, informationsuch as one or more of the age of the patient, the gender of thepatient, and the date of implant are stored in the device by being inputby the implanting physician using a programmer. In addition, the initialfrequency at which lead integrity monitoring, such as impedancemonitoring, for example, may also be set by the physician via theprogrammer, or a default starting frequency may be utilized. Accordingto one embodiment, the device may be initially programmed, either bydefault or by the physician, so that lead integrity monitoring usingimpedance measurements is performed four times per day, and may beincreased once one or more of these patient characteristics aresatisfied, as described in detail below. Once a predetermined period oftime or a predetermined event occurs subsequent to the implant, updatingof the frequency of the lead integrity monitoring according to thepresent disclosure is determined. For example, according to anembodiment, lead integrity issues may be monitored using impedancemeasurements taken four times per day, and the device performs thedetermination 200 of whether to update the lead integrity monitoringfrequency once per day, i.e. once every 24 hours. However, the frequencyof the lead impedance monitoring and/or the frequency at which thedetermination of whether to update the lead integrity monitoringfrequency 200 may also initially be performed at other desiredfrequencies, such as twice a day or once every two days, for example.

As illustrated in FIG. 3, according to an embodiment of the presentdisclosure, the device monitors lead integrity using lead impedancemeasurements taken four times per day, and initially makes thedetermination as to whether to update the lead integrity monitoringfrequency 200 by determining whether the predetermined period of time,i.e., 24 hours, has expired since implant of the device, Block 204. Ifthe update time period has not expired, NO in Block 204, no monitoringfrequency update is performed, Block 206. Once the initial update timehas expired, YES in Block 204, the device determines the current age ofthe patient, compares the patient's current age to a predeterminedpatient age adjustment threshold, and determines whether to update thefrequency at which the lead integrity monitoring is performed based onthe determined age of the patient, Block 208.

For example, in order to determine whether a patient age adjustment isto occur, Block 208, the device determines whether the age of thepatient is within a predetermined patient age range. According to oneembodiment, the patient age range is less than twenty years. Otherpatient age ranges may be utilized, such as whether the age of thepatient is greater than 20 years but less than 40 years. If the currentpatient age is not within the patient range, NO in Block 208, no updateof the frequency of performance of the lead integrity monitoring ismade, Block 206, the device continues performing the lead integritymonitoring at the current monitoring frequency, and waits until the nextfrequency update monitoring is scheduled to occur, Block 204, i.e., thedevice again waits for 24 hours, and the process is repeated.

If the patient is determined to be within the predetermined patient agerange, YES in Block 208, a patient age adjustment is determined to beneeded. According to one embodiment, the device stores a valueassociated with the virtual lead days since implant of the device, whichis initially equal to the running actual or “real days” since implant ofthe device, Block 202. If the patient age adjustment is determined to beneeded, YES in Block 208, the device updates the number of virtual leaddays since implant of the lead, Block 210, by increasing the number ofvirtual lead days, Block 202, by a predetermined number of daysassociated with a patient age adjustment. Therefore, the value of thevirtual days becomes the sum of the running real days since implant ofthe device and the predetermined number of days associated with thepatient age adjustment.

The device may update the stored virtual lead days, Block 210, byincreasing the virtual lead days by a predetermined amount when thepatient is determined to be within the patient adjustment range, Block208. In one embodiment the device increases the virtual lead days, Block210, by adding four days, to the currently stored virtual lead days, forexample. In this way, for each day the patient is determined to be inthe predetermined patient age range, YES in Block 208, the storedvirtual lead days is updated in Block 210 by being increased by fourdays.

Once the virtual lead days have been updated in Block 210, the devicecompares the updated virtual lead days to a virtual lead days thresholdto determine whether the value of updated virtual lead days is greaterthan the virtual lead days threshold, Block 212. If the updated virtuallead days is not greater than the virtual lead days threshold, NO inBlock 212, no monitoring frequency update is performed, Block 206, andthe process is repeated once the next predetermined period of time,i.e., 24 hours has expired, YES in Block 204. If the current updatedvirtual lead days is determined to be greater than the virtual lead daysthreshold, YES in Block 212, the frequency of the lead integritymonitoring is updated by a patient age adjustment value, Block 214, andthe process is repeated once the next predetermined period of time,i.e., 24 hours has expired, YES in Block 204.

According to one embodiment of the disclosure, the virtual lead daysthreshold may be set as five years so that the frequency of the leadintegrity monitoring is increased in Block 214 once the stored updatedvirtual lead days is determined to be greater than five years, Block212. The frequency of the lead integrity monitoring may be updated byincreasing the number of daily impedance measurements used to evaluatelead integrity. In one embodiment, the device increases the number ofdaily impedance values utilized to determine lead integrity issues fromthe initial four impedance values per day to eight values per day.

As illustrated in FIG. 3, the determination of whether to update thelead integrity monitoring frequency 200 of the present invention occursonce every 24 hours, and includes updating the stored virtual lead daysif the patient is determined to be within the patient age range, Block208, and updating the lead monitoring frequency if the stored updatedvirtual lead days is greater than the virtual lead days threshold, Block212. FIG. 4 is a timeline illustrating updating of the frequency of leadintegrity monitoring according to an embodiment of the presentdisclosure. As illustrated in FIG. 4, in order to update the frequencyof lead integrity monitoring, the device increases the number of dailyimpedance values utilized to determine lead integrity issues, indicatedon the upper portion of timeline 220, from the initial four impedancevalues determined per day 222 to eight impedance values determined perday 224 once the accumulated virtual days, indicated on the lowerportion of timeline 220, are greater than 5 years 226. The device thensubsequently increases the number of daily impedance values utilized todetermine lead integrity issues to twelve impedance values determinedper day 228 once the accumulated virtual days are greater than ten years230, to twenty-four impedance values determined per day 232 once theaccumulated virtual days are greater than fifteen years 234, tothirty-six impedance values determined per day 236 once the accumulatedvirtual days are greater than twenty years 238, and to forty-eightimpedance values determined per day 240 once the accumulated virtualdays are greater than twenty-five years 242, and so forth.

FIG. 5 is a flowchart of an exemplary method of determining leadintegrity monitoring frequency in a medical device according to anembodiment of the disclosure. As described above, many factors existthat may contribute to lead failure. According to an embodiment of thepresent disclosure, multiple patient characteristics may be utilized inorder to perform the determination of lead integrity monitoringfrequency. For example, as illustrated in FIG. 5, according to oneembodiment, similar to the embodiment described above, the devicemonitors lead integrity using lead impedance measurements taken fourtimes per day, and initially makes the determination as to whether toupdate the lead integrity monitoring frequency 300 by determiningwhether the predetermined period of time, i.e., 24 hours, has expiredsince implant of the device, Block 304.

If the update time period has not expired, NO in Block 304, nomonitoring frequency update is performed, Block 306. Once the initialupdate time has expired, YES in Block 304, the device determines thecurrent age of the patient, compares the patient's current age to apredetermined patient age adjustment threshold, and determines whetherto adjust the frequency at which the lead integrity monitoring isperformed based on the determined age of the patient, Block 308.

For example, in order to determine whether a patient age adjustment isto occur, Block 308, the device determines whether the age of thepatient is within a predetermined patient age range, such as whether theage of the patient is greater than 20 years but less than 40 years. Ifthe patient is determined to be within the predetermined patient agerange, less than 20 years, for example, YES in Block 308, a patient ageadjustment is determined to be needed. As described above, according toone embodiment, the device stores a value associated with the virtuallead days since implant of the device, which is initially equal to therunning actual or “real days” since implant of the device, Block 302. Ifthe patient age adjustment is determined to be needed, YES in Block 308,the device updates the number of virtual lead days since implant of thelead, Block 310, by increasing the number of virtual lead days by apredetermined number of days associated with a patient age adjustment.According to one embodiment, the device updates the stored virtual leaddays, Block 310, by increasing the virtual lead days by a predeterminedamount when the patient is determined to be within the patientadjustment range, Block 308. In one embodiment the device increases thevirtual lead days, Block 310, by adding four days to the currentlystored virtual lead days, for example. In this way, for each day thepatient is determined to be in the predetermined patient age range, YESin Block 308, the stored virtual lead days is updated in Block 310 bybeing increased by four days. If the patient is determined to not be inthe predetermined patient age range, NO in Block 308, no patient ageadjustment to the virtual days is made.

Once the virtual lead days has been updated based on the patient's agein Block 310, or if the current patient age is not within the patientrange, and therefore a patient age adjustment is not determined to beneeded, NO in Block 308, the device determines the daily level ofactivity of the patient via electrical activity sensed via activitysensor 109 (FIG. 2), compares the patient's daily activity level to apredetermined activity level adjustment threshold, and determineswhether to adjust the frequency at which the lead integrity monitoringis performed based on the determined activity level of the patient,Block 312.

For example, in order to determine whether a patient daily activitylevel adjustment is to occur, Block 312, the device determines whetherthe level of activity of the patient during the most recent time periodassociated with the determination in Block 304 as to whether to updatethe lead integrity monitoring frequency 300, i.e., 24 hours for example,is greater than the patient activity adjustment threshold. According toone embodiment, the patient activity adjustment threshold may be set atpredetermined period of time, such as 400 minutes for example. If thepatient activity is greater than the patient activity adjustmentthreshold and therefore a patient activity adjustment is determined tobe needed, YES in Block 312, the device updates the number of virtuallead days since implant of the lead, Block 314, by increasing the numberof virtual lead days by a predetermined number of days associated with apatient activity adjustment. In one embodiment the device increases thevirtual lead days, Block 314, by adding one real lead day to thecurrently stored virtual lead days, for example. In this way, if thepatient is determined to be engage in the predetermined level ofactivity, YES in Block 312, the stored accumulated virtual lead dayssince implant is updated in Block 314 by being increased a predeterminednumber of days. Therefore, the value of the virtual days includes thesum of the running real days since implant of the device and either orboth the predetermined number of days associated with the patient ageadjustment and the determined number of days associated with the patientactivity, if applicable.

Once either the patient activity is determined to be not greater thanthe patient activity adjustment threshold, and therefore a patientactivity adjustment is not determined to be needed, NO in Block 312, orthe virtual lead days have been updated in Block 314, the devicecompares the updated virtual lead days to a virtual lead days thresholdto determine whether the value of updated virtual lead days is greaterthan the virtual lead days threshold, Block 316. If the updated virtuallead days is not greater than the virtual lead days threshold, NO inBlock 316, no monitoring frequency update is performed, Block 306, andthe process is repeated once the next predetermined period of time,i.e., 24 hours has expired, YES in Block 304. If the current value ofthe updated virtual lead days is determined to be greater than thevirtual lead days threshold, YES in Block 316, a monitoring frequencyupdate is performed so that the frequency of the lead integritymonitoring is updated by a predetermined adjustment value, Block 318,and the process is repeated once the next predetermined period of time,i.e., 24 hours has expired, YES in Block 304.

As described above, according to one embodiment of the disclosure, thevirtual lead days threshold may be set as five years so that thefrequency of the lead integrity monitoring is increased in Block 318once the stored updated virtual lead days is determined to be greaterthan five years, Block 316. The frequency of the lead integritymonitoring may be updated by increasing the number of daily impedancemeasurements used to evaluate lead integrity. In one embodiment, thedevice increases the number of daily impedance values utilized todetermine lead integrity issues from the initial four impedance valuesper day to eight values per day.

As described above, according to another embodiment illustrated in FIG.4, in order to update the frequency of lead integrity monitoring, Block318, as a result of the accumulation of patient age and patientactivity, the device increases the number of daily impedance valuesutilized to determine lead integrity issues, indicated on the upperportion of timeline 220, from the initial four impedance valuesdetermined per day 222 to eight impedance values determined per day 224once the accumulated virtual days, indicated on the lower portion oftimeline 220, are greater than 5 years 226. The device then subsequentlyincreases the number of daily impedance values utilized to determinelead integrity issues to twelve impedance values determined per day 228once the accumulated virtual days are greater than ten years 230, totwenty-four impedance values determined per day 232 once the accumulatedvirtual days are greater than fifteen years 234, to thirty-six impedancevalues determined per day 236 once the accumulated virtual days aregreater than twenty years 238, and to forty-eight impedance valuesdetermined per day 240 once the accumulated virtual days are greaterthan twenty-five years 242, and so forth.

FIG. 6 is a flowchart of an exemplary method of determining leadintegrity monitoring frequency in a medical device according to anembodiment of the disclosure. As illustrated in FIG. 6, according to oneembodiment, similar to the embodiments described above, the devicemonitors lead integrity using lead impedance measurements taken fourtimes per day, and initially makes the determination as to whether toupdate the lead integrity monitoring frequency 400 by determiningwhether the predetermined period of time, i.e., 24 hours, has expiredsince implant of the device, Block 404.

If the update time period has not expired, NO in Block 404, nomonitoring frequency update is performed, Block 406. Once the initialupdate time has expired, YES in Block 404, the device determines thecurrent age of the patient, compares the patient's current age to apredetermined patient age adjustment threshold, and determines whetherto adjust the frequency at which the lead integrity monitoring isperformed based on the determined age of the patient, Block 408.

For example, in order to determine whether a patient age adjustment isto occur, Block 408, the device determines whether the age of thepatient is within a predetermined patient age range, such as whether theage of the patient is greater than 20 years but less than 40 years. Ifthe patient is determined to be within the predetermined patient agerange, i.e., less than twenty years for example, YES in Block 408, apatient age adjustment is determined to be needed. As described above,according to one embodiment, the device stores a value associated withthe virtual lead days since implant of the device, which is initiallyequal to the running actual or “real days” since implant of the device,Block 402. If the patient age adjustment is determined to be needed, YESin Block 408, the device updates the number of virtual lead days sinceimplant of the lead, Block 410, by increasing the number of virtual leaddays by a predetermined number of days associated with a patient ageadjustment. According to one embodiment, the device updates the storedvirtual lead days, Block 410, by increasing the virtual lead days by apredetermined amount when the patient is determined to be within thepatient adjustment range, Block 408. In one embodiment the deviceincreases the virtual lead days, Block 410, by adding four times thenumber of real lead days, Block 402, to the currently stored virtuallead days, for example. In this way, if the patient is determined to bein the predetermined patient age range, YES in Block 408, the virtuallead days since implant is updated in Block 410 by being increased byfour times the number of real lead days, Block 402, since implant of thedevice. If the patient is determined to not be in the predeterminedpatient age range, NO in Block 408, no patient age adjustment to thevirtual days is made.

Once the virtual lead days has been updated based on the patient's agein Block 410, or if the current patient age is not within the patientrange and therefore a patient age adjustment is not determined to beneeded, NO in Block 408, the device determines the daily level ofactivity of the patient via electrical activity sensed via activitysensor 109 (FIG. 2), compares the patient's daily activity level to apredetermined activity level adjustment threshold, and determineswhether to adjust the frequency at which the lead integrity monitoringis performed based on the determined activity level of the patient,Block 412.

For example, in order to determine whether a patient daily activitylevel adjustment is to occur, Block 412, the device determines whetherthe level of activity of the patient during the most recent time periodassociated with the determination in Block 404 as to whether update thelead integrity monitoring frequency 400, i.e., 24 hours for example, isgreater than the patient activity adjustment threshold. According to oneembodiment, the patient activity adjustment threshold may be set atpredetermined period of time, such as 400 minutes for example. Accordingto another embodiment, the activity sensor may generate a signalcorresponding to the number of steps the patient takes per day, andtherefore the patient activity adjustment threshold may be set as 8,000steps per day. If the patient activity is greater than the patientactivity adjustment threshold and therefore a patient activityadjustment is determined to be needed, YES in Block 412, the deviceupdates the number of virtual lead days since implant of the lead, Block414, by increasing the number of virtual lead days by a predeterminednumber of days associated with a patient activity adjustment. Forexample, in one embodiment the device increases the virtual lead days,Block 414, by adding one real lead day to the currently stored virtuallead days, for example. In this way, if the patient is determined to beengage in the predetermined level of activity, YES in Block 412, thestored virtual lead days since implant is updated in Block 414 by beingincreased a predetermined number of days.

Another factor that may contribute to the possible occurrence of leadfailure is the amount of flexing of the lead that occurs. As the numberof times the lead is flexed increases, the possibility of lead failuremay increase. Therefore, according to one embodiment, in addition tobeing updated in response to patient age and activity, the device mayalso utilize the patient heart rate, as a metric of the number of leadflexes that occur over the lifetime of the lead, as an indicator ofwhether to update the frequency of lead integrity monitoring. Forexample, the device may determine the number of cardiac cycles viaactivity sensor 109 (FIG. 2), compares the number of cardiac cycles to apredetermined cardiac cycle adjustment threshold, and determines whetherto adjust the frequency at which the lead integrity monitoring isperformed based on the determined number of cardiac cycles that occurduring a given time period, Block 416.

For example, in order to determine whether a number of cardiac cycleadjustment is to occur, Block 416, the device determines whether thenumber of cardiac cycles of the patient during the most recent timeperiod associated with the determination in Block 404 as to whether toupdate the lead integrity monitoring frequency 400, i.e., 24 hours forexample, is greater than the cardiac cycle adjustment threshold.According to one embodiment, the cardiac cycle adjustment threshold isset at predetermined number of cardiac cycles, such as 10,000 cycles,for example. If the number of cardiac cycles is greater than the cardiaccycle adjustment threshold and therefore a patient cardiac cycleadjustment is determined to be needed, YES in Block 416, the deviceupdates the number of virtual lead days since implant of the lead, Block418, by increasing the number of virtual lead days by a predeterminednumber of days associated with a patient cardiac cycle adjustment. Inone embodiment the device increases the virtual lead days, Block 418, byadding one real lead day to the currently stored virtual lead days, forexample. Therefore, the value of the virtual days includes the sum ofthe running real days since implant of the device and either one or acombination of the predetermined number of days associated with thepatient age adjustment, the determined number of days associated withthe patient activity adjustment and the determined number of daysassociated with patient cardiac cycle adjustment, if applicable.

Once at least one of the patient age, patient activity, and number ofcardiac cycles and determined and the virtual lead days updatedaccordingly, Blocks 408-418, the device compares the updated virtuallead days to a virtual lead days threshold to determine whether thevalue of updated virtual lead days is greater than the virtual lead daysthreshold, Block 420. If the updated virtual lead days is not greaterthan the virtual lead days threshold, NO in Block 420, no monitoringfrequency update is performed, Block 406, and the process is repeatedonce the next predetermined period of time, i.e., 24 hours has expired,YES in Block 404. If the current value of the updated virtual lead daysis determined to be greater than the virtual lead days threshold, YES inBlock 420, a monitoring frequency update is performed so that thefrequency of the lead integrity monitoring is updated by a predeterminedadjustment value, Block 422, and the process is repeated once the nextpredetermined period of time, i.e., 24 hours has expired, YES in Block404.

As described above, according to one embodiment of the disclosure, thevirtual lead days threshold may be set as five years so that thefrequency of the lead integrity monitoring is increased in Block 422once the stored updated virtual lead days is determined to be greaterthan five years, Block 420. The frequency of the lead integritymonitoring may be updated by increasing the number of daily impedancemeasurements used to evaluate lead integrity. In one embodiment, thedevice increases the number of daily impedance values utilized todetermine lead integrity issues from the initial four impedance valuesper day to eight values per day.

As described above, according to another embodiment illustrated in FIG.4, in order to update the frequency of lead integrity monitoring, Block422, as a result of the accumulation of patient age and patientactivity, the device increases the number of daily impedance valuesutilized to determine lead integrity issues, indicated on the upperportion of timeline 220, from the initial four impedance valuesdetermined per day 222 to eight impedance values determined per day 224once the accumulated virtual days, indicated on the lower portion oftimeline 220, are greater than 5 years 226. The device then subsequentlyincreases the number of daily impedance values utilized to determinelead integrity issues to twelve impedance values determined per day 228once the accumulated virtual days are greater than ten years 230, totwenty-four impedance values determined per day 232 once the accumulatedvirtual days are greater than fifteen years 234, to thirty-six impedancevalues determined per day 236 once the accumulated virtual days aregreater than twenty years 238, and to forty-eight impedance valuesdetermined per day 240 once the accumulated virtual days are greaterthan twenty-five years 242, and so forth.

FIG. 7 is a flowchart of an exemplary method of determining leadintegrity monitoring frequency in a medical device according to anembodiment of the disclosure. As illustrated in FIG. 7, according toanother embodiment, the device monitors lead integrity using leadimpedance measurements taken four times per day, and initially makes thedetermination as to whether to update the lead integrity monitoringfrequency 500 by determining whether the predetermined period of time,i.e., 24 hours, has expired since implant of the device, Block 504.

If the update time period has not expired, NO in Block 504, nomonitoring frequency update is performed, Block 506. Once the initialupdate time has expired, YES in Block 504, the device determines thecurrent age of the patient, compares the patient's current age to apredetermined patient age adjustment threshold, and determines whetherto adjust the frequency at which the lead integrity monitoring isperformed based on the determined age of the patient, Block 508.

For example, in order to determine whether a patient age adjustment isto occur, Block 508, the device determines whether the age of thepatient is within a predetermined patient age range, such as whether theage of the patient is less than 20 years, for example. If the patient isdetermined to be within the predetermined patient age range, YES inBlock 508, a patient age adjustment is determined to be needed. Asdescribed above, according to one embodiment, the device stores a valueassociated with the virtual lead days since implant of the device, whichis initially equal to the running actual or “real days” since implant ofthe device, Block 502. If the patient age adjustment is determined to beneeded, YES in Block 508, the device updates the number of virtual leaddays since implant of the lead, Block 510, by increasing the number ofvirtual lead days by a predetermined number of days associated with apatient age adjustment. According to one embodiment, the device updatesthe stored virtual lead days, Block 510, by increasing the virtual leaddays by a predetermined amount when the patient is determined to bewithin the patient adjustment range, Block 508. In one embodiment thedevice increases the virtual lead days, Block 510, by adding four timesthe number of real lead days, Block 502, to the currently stored virtuallead days, for example. In this way, if the patient is determined to bein the predetermined patient age range, YES in Block 508, the virtuallead days since implant is updated in Block 510 by being increased byfour times the number of real lead days, Block 502, since implant of thedevice. If the patient is determined to not be in the predeterminedpatient age range, NO in Block 508, no patient age adjustment to thevirtual days is made. Therefore, the value of the virtual days includesthe sum of the running real days since implant of the device and thepredetermined number of days associated with the patient age adjustment,if applicable.

Once the virtual lead days has been updated based on the patient's agein Block 510, or if the current patient age is not within the patientrange, and therefore a patient age adjustment is not determined to beneeded, NO in Block 508, the device determines the daily level ofactivity of the patient via electrical activity sensed via activitysensor 109 (FIG. 2), compares the patient's daily activity level to apredetermined activity level adjustment threshold, and determineswhether to adjust the frequency at which the lead integrity monitoringis performed based on the determined activity level of the patient,Block 512.

For example, in order to determine whether a patient daily activitylevel adjustment is to occur, Block 512, the device determines whetherthe level of activity of the patient during the most recent time periodassociated with the determination in Block 504 as to whether to updatethe lead integrity monitoring frequency 300, i.e., 24 hours for example,is greater than the patient activity adjustment threshold. According toone embodiment, the patient activity adjustment threshold may be set atpredetermined period of time, such as 400 minutes for example. If thepatient activity is greater than the patient activity adjustmentthreshold and therefore a patient activity adjustment is determined tobe needed, YES in Block 512, the device updates the number of virtuallead days since implant of the lead, Block 514, by increasing the numberof virtual lead days by a predetermined number of days associated with apatient activity adjustment. In one embodiment the device increases thevirtual lead days, Block 514, by adding one real lead day to thecurrently stored virtual lead days, for example. In this way, if thepatient is determined to be engaged in the predetermined level ofactivity, YES in Block 512, the stored accumulated virtual lead dayssince implant is updated in Block 514 by being increased a predeterminednumber of days. As described above, two factors that may contribute tothe occurrence of issues leading to failure of the lead are the age andthe level of activity of the patient, with an increase in the number oflead integrity issues occurring for younger patients and patients whoare more active. Since both factors may contribute to increased risk ofintegrity issues occurring, there may be reason to include a weightingof how these factors are considered in determining integrity monitoringfrequency. For example, a patient who is within the increased risk agegroup and is relatively active may need to be distinguished from aperson within the increased risk age group who is extremely active. Inaddition, a person outside the increased risk age group may be so activethat the risk of lead integrity issues for that person may be similar tothe person who is within the increased risk age group but who is onlyrelatively active. Therefore, according to one embodiment, once thedevice determines that the patient is within the patient age range, YESin Block 508, that a patient activity level adjustment is necessary, YESin Block 512, and updates the value of the virtual lead daysaccordingly, Blocks 510 and 514, the device may determine whether anincreased patient activity level adjustment to the stored virtual leaddays should be made, Block 516.

In particular, in order to distinguish extremely active and relativelyactive patients who have both been identified as being within theincreased risk age group, the device compares the patient's dailyactivity level to a second predetermined activity level adjustmentthreshold, Block 516, that is greater than the first activity leveladjustment threshold previously utilized in Block 512. According to oneembodiment, the first activity level adjustment threshold associatedwith the first patient activity adjustment determination, Block 512, isset at 400 minutes, as described above, and the second patient activitylevel adjustment threshold associated with the second patient activityadjustment determination, Block 516, is set at 450 minutes, for example.

If the patient activity level is greater than the second patientactivity adjustment threshold, YES in Block 516, and therefore anincreased patient activity adjustment is determined to be needed, thedevice updates the number of virtual lead days since implant of thelead, Block 518, a second time by further increasing the number ofvirtual lead days by a predetermined number of days associated with anextreme patient activity adjustment. In one embodiment the deviceadditionally increases the virtual lead days, Block 518, by adding onereal lead day to the currently stored virtual lead days, for example. Inthis way, if the patient is determined to be engage in the predeterminedextreme level of activity, YES in Block 516, the stored accumulatedvirtual lead days since implant is further updated by being increased anadditional predetermined number of days.

According to another embodiment, in order to identify a patient who isoutside the increased risk age group who nevertheless may be so activethat the risk of lead integrity issues for that patient may be similarto the patient who is within the increased risk age group, if the devicedetermines that the current patient age is not within the patient range,and therefore a patient age adjustment is not determined to be needed,NO in Block 508, but a patient activity adjustment is determined to beneeded, YES in Block 512, and therefore the device updates the number ofvirtual lead days since implant of the lead, Block 514, by increasingthe number of virtual lead days by a predetermined number of daysassociated with a patient activity adjustment, the devices then comparesthe patient's daily activity level to a second predetermined activitylevel adjustment threshold, Block 516, that is greater than the firstactivity level adjustment threshold previously utilized in Block 512.According to this embodiment, the first activity level adjustmentthreshold associated with the first patient activity adjustmentdetermination, Block 512, is set at 400 minutes, as described above, andthe second patient activity level adjustment threshold associated withthe second patient activity adjustment determination, Block 516, is setbeing weighted based on the amount that the activity level is greaterthan the first activity level adjustment threshold previously utilizedin Block 512. For example, according to one embodiment, the storedvirtual days are increased a predetermined number of days for eachpredetermined number of minutes that the activity level is greater thanthe first activity level adjustment threshold previously utilized inBlock 512, i.e. greater than 400 minutes. In one embodiment the storedvirtual days may be increased one day for each 50 minutes of activitygreater than the first activity level adjustment threshold previouslyutilized in Block 512. Therefore, the stored virtual days are increasedan additional day once the activity level reaches 450 minutes, forexample, or four additional days if the activity level reaches 600minutes.

Once either the patient activity is determined to be not greater thanthe patient activity adjustment threshold, and therefore a patientactivity adjustment is not determined to be needed, NO in Block 512, orthe virtual lead days have been updated in Block 514 or in both Block514 and Block 518, the device compares the resulting updated virtuallead days to a virtual lead days threshold to determine whether thevalue of updated virtual lead days is greater than the virtual lead daysthreshold, Block 520. If the updated virtual lead days is not greaterthan the virtual lead days threshold, NO in Block 520, no monitoringfrequency update is performed, Block 506, and the process is repeatedonce the next predetermined period of time, i.e., 24 hours has expired,YES in Block 504. If the current value of the updated virtual lead daysis determined to be greater than the virtual lead days threshold, YES inBlock 520, a monitoring frequency update is performed so that thefrequency of the lead integrity monitoring is updated by a predeterminedadjustment value, Block 522, and the process is repeated once the nextpredetermined period of time, i.e., 24 hours has expired, YES in Block504.

As described above, according to one embodiment of the disclosure, thevirtual lead days threshold may be set as five years so that thefrequency of the lead integrity monitoring is increased in Block 522once the stored updated virtual lead days is determined to be greaterthan five years, YES in Block 520. The frequency of the lead integritymonitoring may be updated by increasing the number of daily impedancemeasurements used to evaluate lead integrity. In one embodiment, thedevice increases the number of daily impedance values utilized todetermine lead integrity issues from the initial four impedance valuesper day to eight values per day.

As described above, according to another embodiment illustrated in FIG.4, in order to update the frequency of lead integrity monitoring, Block522, the device increases the number of daily impedance values utilizedto determine lead integrity issues, indicated on the upper portion oftimeline 220, from the initial four impedance values determined per day222 to eight impedance values determined per day 224 once theaccumulated virtual days, indicated on the lower portion of timeline220, are greater than 5 years 226. The device then subsequentlyincreases the number of daily impedance values utilized to determinelead integrity issues to twelve impedance values determined per day 228once the accumulated virtual days are greater than ten years 230, totwenty-four impedance values determined per day 232 once the accumulatedvirtual days are greater than fifteen years 234, to thirty-six impedancevalues determined per day 236 once the accumulated virtual days aregreater than twenty years 238, and to forty-eight impedance valuesdetermined per day 240 once the accumulated virtual days are greaterthan twenty-five years 242, and so forth.

FIG. 8 is a flowchart of an exemplary method of determining leadintegrity monitoring frequency in a medical device according to anembodiment of the disclosure. According to one embodiment, the number ofcardiac cycles may be utilized in place of patient activity or incombination with patient activity, as shown in FIG. 8. For the sake ofbrevity, the determination of whether the patient is within the patientage range and/or is determined to have a predetermined level activity,Blocks 602-618 of FIG. 8 have been described above in reference to FIG.7 and will not be repeated.

As illustrated in FIG. 8, As illustrated in FIG. 8, the device may alsodetermine the number of cardiac cycles via activity sensor 109 (FIG. 2),compare the number of cardiac cycles to a predetermined cardiac cycleadjustment threshold, and determine whether to adjust the frequency atwhich the lead integrity monitoring is performed based on the determinednumber of cardiac cycles that occur during a given time period, Block620.

For example, in order to determine whether a number of cardiac cycleadjustment is to occur, Block 620, the device determines whether thenumber of cardiac cycles of the patient during the most recent timeperiod associated with the determination in Block 604 as to whether toupdate the lead integrity monitoring frequency 400, i.e., 24 hours forexample, is greater than the cardiac cycles adjustment threshold.According to one embodiment, the cardiac cycles adjustment threshold maybe set at predetermined number of cardiac cycles, such as 100,000cycles, for example. If the number of cardiac cycles is greater than thecardiac cycles adjustment threshold and therefore a patient cardiaccycles adjustment is determined to be needed, YES in Block 620, thedevice updates the number of virtual lead days since implant of thelead, Block 622, by increasing the number of virtual lead days by apredetermined number of days associated with a patient cardiac cyclesadjustment. In one embodiment the device increases the virtual leaddays, Block 622, by adding one real lead day to the currently storedvirtual lead days, for example.

According to the embodiment of FIG. 8, in order to distinguish extremelyactive and relatively active patients who have both been identified asbeing within the increased risk age group, the device compares thepatient's determined number of cardiac cycles to a second cardiac cyclesadjustment threshold, Block 624, that is greater than the first cardiaccycles adjustment threshold previously utilized in Block 620. Accordingto one embodiment, the first cardiac cycles adjustment thresholdassociated with the first patient cardiac cycles adjustmentdetermination, Block 620, is set at 100,000 cardiac cycles, as describedabove, and the second patient cardiac cycles adjustment thresholdassociated with the second patient cardiac cycles adjustmentdetermination, Block 624, is set at 110,000 cardiac cycles, for example.

If the number of cardiac cycles is greater than the second cardiaccycles adjustment threshold, YES in Block 624, and therefore anincreased patient activity adjustment is determined to be needed, thedevice updates the number of virtual lead days since implant of thelead, Block 626, a second time by further increasing the number ofvirtual lead days by a predetermined number of days associated with anextreme patient cardiac cycles adjustment. In one embodiment the deviceadditionally increases the virtual lead days, Block 626, by adding onehalf of real lead day to the currently stored virtual lead days, forexample.

According to another embodiment, the second patient cardiac cyclesadjustment threshold associated with the second patient cardiac cyclesadjustment determination, Block 624, may be set being weighted based onthe amount that the number of cardiac cycles are greater than the firstcardiac cycles adjustment threshold previously utilized in Block 620.For example, according to one embodiment, the stored virtual days areincreased a predetermined number of days for each predetermined numberof minutes that the number of cardiac cycles are greater than the firstcardiac cycles adjustment threshold previously utilized in Block 620,i.e. greater than 100,000 cycles. In one embodiment the stored virtualdays may be increased one half of a day for each 10,000 cycles that thenumber of cardiac cycles are greater than the first cardiac cyclesadjustment threshold previously utilized in Block 620. Therefore, thestored virtual days are increased an additional half-day once the numberof cardiac cycles reaches 110,000 cycles, for example, or two additionaldays if the number of cardiac cycles reaches 140,000 cardiac cycles.

FIG. 9 is a flowchart of an exemplary method of determining leadintegrity monitoring frequency in a medical device according to anembodiment of the disclosure. In certain instances, such as when abattery becomes depleted, it may become necessary for the device to beremoved from the patient and replaced by a replacement device.Typically, as long as the lead of the device is still in a satisfactoryoperable condition, this “device change out” involves disconnecting thelead from the header of the housing, or can of the device, and removingand replacing only the removed housing. If the device being removed andreplaced included and utilized the method and apparatus for determininglead integrity monitoring frequency described above, the value of theupdated virtual lead days may simply be transferred from the devicebeing removed to the new device being implanted, and the determinationof whether to update the lead integrity monitoring frequency describedabove would continue. However, if the apparatus for determining leadintegrity monitoring frequency described above was not included orutilized in the device being removed and replaced by a new device, itmay be necessary to initialize the virtual days in the replacementdevice to be updated to account for the time period that the lead wasutilized while connected to the device being explanted.

Therefore, as illustrated in FIG. 9, during implant of the replacementdevice within the patient and connection of the replacement devicehousing to the prior implanted lead, information such as one or more ofthe age of the patient, the gender of the patient, the date of implantof the device currently being explanted, the date of implant of theimplanted lead, and the date of implant of the replacement device may bestored in the replacement device by being input by the implantingphysician using a programmer. In addition, the initial frequency atwhich lead integrity monitoring, such as impedance monitoring, forexample, is performed may also be set by the physician via theprogrammer, or a default starting frequency may be utilized. The numberof days since the implant of the explanted device and the number of dayssince implant of the lead, Block 702, is either determined by thephysician at the time of the implant of the replacement device and inputin the replacement device by the physician, or may be determined by thereplacement device using the stored date of the explanted device. Ofcourse, unless more than one explant procedure has occurred, the numberof days since implant of the explanted device, i.e., the housing or can,is the same as the number of days since implant of the lead, since bothwere implanted at the same time.

The replacement device updates the virtual lead days, Block 704, whichis initially set equal to the running actual or “real days” sinceimplant of the replacement device, by increasing the value of the storedvirtual lead days by the number of days since the implant of theexplanted device. For example, if the explanted device was removed fouryears after being implanted and replaced by the replacement device, thereplacement device would set the initial value of the stored virtuallead days to four years.

If the current device explant and replacement procedure is not the firstexplant procedure associated with the lead at issue, meaning that theexplanted housing or can is not the same housing or can that wasinitially implanted simultaneously with the lead, additional informationsuch as the date that the lead was implanted may also be determined, ifsuch information is available.

As illustrated in FIG. 9, once the initial value of the virtual leaddays is updated in Block 704 to reflect the life of the lead whileconnected to the explanted device, or if the current explant change outprocedure is not the first explant procedure to take place, to reflectthe actual period of time the lead has been implanted, updating of thefrequency of lead integrity monitoring may be determined in ways similarto any of the embodiments described above. For example, according to oneembodiment, lead integrity issues may be monitored using impedancemeasurements taken four times per day, and the device performs thedetermination 700 of whether to update the lead integrity monitoringfrequency once per day, i.e. once every 24 hours. However, the frequencyof the lead impedance monitoring and/or the frequency at which thedetermination of whether to update the lead integrity monitoringfrequency 700 may also initially be performed at other desiredfrequencies, such as twice a day or once every two days, for example.

Therefore, as illustrated in FIG. 9, according to an embodiment of thepresent disclosure, the replacement device monitors lead integrity usinglead impedance measurements taken four times per day, and initiallymakes the determination as to whether to update the lead integritymonitoring frequency 700 by determining whether the predetermined periodof time, i.e., 24 hours, has expired since implant of the device, Block708. If the update time period has not expired, NO in Block 708, nomonitoring frequency update is performed, Block 710. Once the initialupdate time has expired, YES in Block 708, the replacement devicedetermines the current age of the patient, compares the patient'scurrent age to a predetermined patient age adjustment threshold, anddetermines whether to update the frequency at which the lead integritymonitoring is performed based on the determined age of the patient,Block 712.

For example, in order to determine whether a patient age adjustment isto occur, Block 712, the replacement device determines whether the ageof the patient is within a predetermined patient age range, such aswhether the age of the patient is less than 20 years. If the currentpatient age is not within the patient range, NO in Block 714, no updateof the frequency of performance of the lead integrity monitoring ismade, Block 710, the replacement device continues performing the leadintegrity monitoring at the current monitoring frequency, and waitsuntil the next frequency update monitoring is scheduled to occur, Block708, i.e., the replacement device again waits for 24 hours, and theprocess is repeated.

If the patient is determined to be within the predetermined patient agerange, YES in Block 712, a patient age adjustment is determined to beneeded. If the patient age adjustment is determined to be needed, YES inBlock 712, the replacement device initially updates the previouslydetermined updated virtual lead days by increasing the value of thenumber of virtual lead days by a predetermined number of days associatedwith a patient age adjustment, Block 714.

The replacement device may update the stored virtual lead days, Block714, by increasing the virtual lead days by a predetermined amount whenthe patient is determined to be within the patient adjustment range,Block 712. In one embodiment the replacement device increases thevirtual lead days, Block 714, by adding four days to the currentlystored virtual lead days, for example. In this way, for each day thepatient is determined to be in the predetermined patient age range, YESin Block 712, the stored virtual lead days is updated in Block 714 bybeing increased by four days.

Once the virtual lead days have been updated in Block 714, thereplacement device compares the updated virtual lead days to a virtuallead days threshold to determine whether the value of updated virtuallead days is greater than the virtual lead days threshold, Block 716. Ifthe updated virtual lead days is not greater than the virtual lead daysthreshold, NO in Block 716, no monitoring frequency update is performed,Block 710, and the process is repeated once the next predeterminedperiod of time, i.e., 24 hours has expired, YES in Block 708. If thecurrent updated virtual lead days are determined to be greater than thevirtual lead days threshold, YES in Block 716, the frequency of the leadintegrity monitoring is updated by a patient age adjustment value, Block718, and the process is repeated once the next predetermined period oftime, i.e., 24 hours has expired, YES in Block 708.

As described above, according to one embodiment of the disclosure, thevirtual lead days threshold may be set as five years so that thefrequency of the lead integrity monitoring is increased in Block 718once the stored updated virtual lead days is determined to be greaterthan five years, Block 716. The frequency of the lead integritymonitoring may be updated by increasing the number of daily impedancemeasurements used to evaluate lead integrity. In one embodiment, thereplacement device increases the number of daily impedance valuesutilized to determine lead integrity issues from the initial fourimpedance values per day to eight values per day.

As described above, according to another embodiment illustrated in FIG.4, in order to update the frequency of lead integrity monitoring, Block718, as a result of the accumulation of the updated lead virtual daysresulting from both the update to account for the time period that thelead was utilized while connected to the replacement device beingexplanted, Block 704 and the determined patient age, Block 714, thereplacement device increases the number of daily impedance valuesutilized to determine lead integrity issues, indicated on the upperportion of timeline 220, from the initial four impedance valuesdetermined per day 222 to eight impedance values determined per day 224once the accumulated virtual days, indicated on the lower portion oftimeline 220, are greater than 5 years 226. The replacement device thensubsequently increases the number of daily impedance values utilized todetermine lead integrity issues to twelve impedance values determinedper day 228 once the accumulated virtual days are greater than ten years230, to twenty-four impedance values determined per day 232 once theaccumulated virtual days are greater than fifteen years 234, tothirty-six impedance values determined per day 236 once the accumulatedvirtual days are greater than twenty years 238, and to forty-eightimpedance values determined per day 240 once the accumulated virtualdays are greater than twenty-five years 242, and so forth.

FIG. 10 is a flowchart of an exemplary method of determining leadintegrity monitoring frequency in a medical device according to anembodiment of the disclosure. During replacement of the device, factorsother than merely the number of days since implant of the lead may beutilized to update the virtual lead days stored in the replacementdevice. Therefore, according to an embodiment, updating of the virtuallead days stored in the replacement device may include the number ofdays since implant of the lead in combination with an additional patientcharacteristic, such as daily activity or number of the cardiac cyclesduring a predetermined period of time, as described above.

For example, as illustrated in FIG. 10, according to one embodiment,during implant of the replacement device within the patient andconnection of the replacement device to the prior implanted lead,information such as one or more of the age of the patient, the gender ofthe patient, the date of implant of the explanted device, and the dateof implant of the replacement device may be stored in the device bybeing input by the implanting physician using a programmer. In addition,the initial frequency at which lead integrity monitoring, such asimpedance monitoring, for example, may also be set by the physician viathe programmer, or a default starting frequency may be utilized. Thenumber of days since the implant of the explanted device, and thereforethe number of days since the implant of the lead (assuming a firstexplant procedure), Block 702, is either determined by the physician atthe time of the implant of the replacement device and input in thereplacement device by the physician, or may be determined by thereplacement device using the stored date of the explanted device. Inaddition, the replacement device may determine one or more patientcharacteristics using data stored in the explanted device, Block 703, tobe utilized in determining the value of the updated virtual lead daysstored in the replacement device.

According to one embodiment, using the age of the patient at implant ofthe explanted device, the replacement device determines the number ofdays that the patient's age was less than a predetermined thresholdprior to the explanted device being removed, Block 703. For example,according to one embodiment, the replacement device uses informationstored in the explanted device (or input by the physician) to determinethe number of days that the patient's age was less than a patient agethreshold prior to the explant procedure, and updates the initial valueof the stored virtual lead days by a predetermined number of days foreach day that the patient's age was less than the patient age threshold.In one embodiment, the replacement device determines the number of daysthat the patient's age was less than twenty years old, and updates thevalue of the stored virtual lead days by four days for each day that thepatient's age was less than the patient age threshold. According toanother embodiment, the replacement device determines the number of daysthat the patient's age was within a range, such as between twenty andforty years, for example, and updates the value of the stored virtuallead days by four days for each day that the patient's age was withinthe patient age range.

The replacement device updates the virtual lead days, Block 704, whichis initially set equal to the running actual or “real days” sinceimplant of the lead, by increasing the current value of the storedvirtual lead days by the sum of the number of days since the implant ofthe lead, Block 702, and the determined patient characteristicadjustment, Block 703. For example, if the explanted device was removedfour years after being implanted and replaced by the replacement device,and the patient was 22 years old at the time of replacement, the numberof days since the implant of the explanted device, Block 702, would befour years (assuming first explant), and the number of days that thepatient's age was within the patient age range (less than 20 years),Block 703, would be 2 years. According to one embodiment, for eachupdate period that the patient is determined to have been in thepredetermined patient age range, the stored virtual lead days is updatedin Block 210 by being increased by four days. Therefore, the patientcharacteristic adjustment to the virtual lead days, Block 703, wouldresult in an adjustment of 8 years (2 years×4=8 years). The replacementdevice therefore would set the initial value of the stored virtual leaddays, Block 704, to twelve years (4 years (real days since initial leadimplant)+8 years (patient characteristic adjustment)).

In the same way, according to another embodiment, the determination ofthe patient character adjustment in Block 703 may include adetermination of the activity level of the patient occurring prior tothe explanted device being removed. For example, assuming a firstexplant procedure and using data stored in the explanted device, thereplacement device may compare data stored in the explanted devicerelating to the patient's daily activity level to a predeterminedactivity level adjustment threshold, and update the value of the storedvirtual lead days in Block 704 accordingly. According to one embodiment,the replacement device determines the number of days that the patientdaily activity level is greater than a predetermined threshold, such as400 minutes for example.

During the updating of the stored virtual lead days in Block 704, if theexplanted device was removed four years after being implanted andreplaced by the replacement device, the patient was 22 years old at thetime of replacement, and the patient had a daily activity level greaterthan the activity level threshold on 100 days, the patientcharacteristic adjustmentin Block 703 would result in an adjustment of 8years (2 years×4=8 years) and 100 days. According to one embodiment, thereplacement device updates the virtual lead days, Block 704, byincreasing the value of the stored virtual lead days by the sum of thenumber of days since the implant of the explanted device, Block 702, andthe determined patient characteristic adjustment, Block 703. Therefore,the replacement device would set the initial value of the stored virtuallead days, Block 704, to twelve years (4 years (days since initiallead/device implant)+(8 years and 100 days) (patient characteristicadjustment)).

These and other patient characteristics having values stored in theexplanted device may also be utilized, alone or in combination, such asthe number of cardiac cycles that occur during a given time period priorto the explanted device being removed. For example, the determination ofthe patient characteristic adjustment, Block 703, may includedetermining the number of cardiac cycles that occur during a given timeperiod, so the replacement device determines the number of times thedaily number of cardiac cycles of the patient was greater than a cardiaccycle adjustment threshold, such as 100,000 cycles, for example. Thereplacement device updates the lead virtual days, Block 704, byincreasing the virtual lead days by one day for each day the number ofdaily cardiac cycles exceed the cardiac cycle adjustment threshold inaddition to the determined number of days since implant of the lead,Block 702, and any other patient characteristics that may be desired inthe patient characteristic adjustment in Block 703.

Once the value of the stored virtual lead days has been update in Block704, the replacement device determines whether to update the leadintegrity monitoring frequency, Blocks 708-718 as described above, andtherefore the description associated with Blocks 708-715 will not berepeated for brevity sake. It is also understood that updating of thestored virtual lead days in the replacement device may include anycombination or single use of the days that the explanted device wasimplanted and or any one or more patient character adjustments availablein the explanted device. In addition, it is also understood that, whilethe updating of the stored virtual lead days in the replacement deviceis shown only in combination with the use of patient activity (similarto FIG. 3) to determine whether to update the lead integrity monitoringfrequency, Blocks 708-718, the updating of the stored virtual lead daysin the replacement device may be utilized in combination with otherembodiments for determining whether to update the lead integritymonitoring frequency, such as any of the embodiments described above.

Thus, a medical device and associated methods for monitoring leadintegrity have been presented in the foregoing description withreference to specific embodiments. Various combinations or modificationsof the illustrative embodiments may be conceived by one having ordinaryskill in the art based on the teachings provided herein. For example,other resolutions for updating of the frequency of lead integritymonitoring may be utilized in addition to those described above inreference to FIG. 4. For example, according to another embodiment, theintegrity monitoring frequency may be increased by two for eachincremental year of virtual lead years. As a result, the integritymonitoring frequency would be increased from four times per day to sixtimes per day once the virtual lead days increased to a year, to eighttimes per day once the virtual lead days increased to two years, to tentimes per day once the virtual lead days reached three years, and soforth. Thus it is appreciated that various modifications to thereferenced embodiments may be made without departing from the scope ofthe disclosure as set forth in the following claims.

We claim:
 1. A medical device, comprising: a device housing containingelectronic circuitry; a lead electrically coupled to the housing; anelectrode positioned along the lead to sense a cardiac signal and todeliver cardiac therapy; and a processor positioned within the housingand configured to determine whether a lead condition is occurring inresponse to the sensed cardiac signal, determine whether a first patientcharacteristic is satisfied during a plurality of predetermined updateperiods, perform a first update of a virtual lead days value associatedwith a number of days since implant of the lead in response to the firstpatient characteristic being satisfied, determine whether a patientcharacteristic update is satisfied in response to a second patientcharacteristic, different than the first patient characteristic, beingsatisfied, perform a second update of the virtual lead days value inresponse to the patient characteristic update being satisfied, andupdate a frequency of determining whether the lead condition isoccurring in response to the updated virtual lead days value.
 2. Themedical device of claim 1, wherein the first patient characteristiccomprises a patient age and the processor is configured to perform thefirst update of the virtual lead days value in response to the patientage being within a predetermined patient age range and to not performthe first update of the virtual lead days value in response to thepatient age being outside the predetermined patient age range.
 3. Themedical device of claim 2, wherein the second patient characteristiccomprises a patient activity level and processor is configured todetermine the patient characteristic update is satisfied in response tothe patient activity level being greater than a predetermined patientactivity level threshold.
 4. The medical device of claim 1, wherein theprocessor is configured to compare the updated virtual lead days to aplurality of predetermined thresholds, and increase the frequency ofdetermining whether the lead condition is occurring in response to thecomparing.
 5. The medical device of claim 1, wherein the second patentcharacteristic comprises a number of cardiac cycles and the processor isconfigured to determine the patient characteristic update is satisfiedin response to the number of cardiac cycles being greater than apredetermined cardiac cycles threshold.
 6. The medical device of claim5, wherein the first patient characteristic comprises a patient age andthe processor is configured to perform the first update of the virtuallead days value in response to the patient age being within apredetermined patient age range and to not perform the first update ofthe virtual lead days value in response to the patient age being outsidethe predetermined patient age range.
 7. The medical device of claim 1,wherein the processor is configured to compare the updated virtual leaddays to a plurality of predetermined thresholds, and increase thefrequency of determining whether the lead condition id occurring inresponse to the comparing.
 8. The medical device of claim 1, whereinsecond patient characteristic comprises a patient activity level and anumber of cardiac cycles, and the processor is configured to determinethe patient characteristic update is satisfied in response to one orboth the patient activity level being greater than a predeterminedpatient activity level threshold and the number of cardiac cycles beinggreater than a predetermined cardiac cycles threshold.
 9. The medicaldevice of claim 8, wherein the first patient characteristic comprises apatient age and the processor is configured to perform the first updateof the virtual lead days value in response to the patient age beingwithin a predetermined patient age range and to not perform the firstupdate of the virtual lead days value in response to the patient agebeing outside the predetermined patient age range.
 10. The medicaldevice of claim 1, wherein the processor is configured to compare theupdated virtual lead days to a plurality of predetermined thresholds,and increase the frequency of determining whether the lead condition isoccurring in response to the comparing.
 11. The medical device of claim1, wherein the processor is configured to determine one or moreimpedance values in response to the delivered therapy a predeterminednumber of times during a predetermined time period, determine whetherthe lead condition is occurring in response to the determined one ormore impedance values, and update the frequency of determining whetherthe lead condition is occurring in response to the increasedpredetermined number of times.
 12. A method for updating a frequency ofdetermining whether a lead condition is occurring in a medical device,comprising: sensing a cardiac signal; determining whether a leadcondition is occurring in response to the sensed cardiac signal;determining whether a first patient characteristic is satisfied during aplurality of predetermined update periods; performing a first update ofa virtual lead days value associated with a number of days since implantof the lead in response to the first patient characteristic beingsatisfied; determining whether a patient characteristic update issatisfied in response to a second patient characteristic, different thanthe first patient characteristic, being satisfied; performing a secondupdate of the virtual lead days value in response to the patientcharacteristic update being satisfied; and updating a frequency ofdetermining whether the lead condition is occurring in response to theupdated virtual lead days value.
 13. The method of claim 12, wherein thefirst patient characteristic comprises a patient age and furthercomprising: performing the first update of the virtual lead days valuein response to the patient age being within a predetermined patient agerange; and not perform the first update of the virtual lead days valuein response to the patient age being outside the predetermined patientage range.
 14. The method of claim 13, wherein the second patientcharacteristic comprises a patient activity level and further comprisingdetermining the patient characteristic update is satisfied in responseto the patient activity level being greater than a predetermined patientactivity level threshold.
 15. The method of claim 12, furthercomprising: comparing the updated virtual lead days to a plurality ofpredetermined thresholds; and increasing the frequency of determiningwhether the lead condition is occurring in response to the comparing.16. The method of claim 12, wherein the second patent characteristiccomprises a number of cardiac cycles and further comprising determiningthe patient characteristic update is satisfied in response to the numberof cardiac cycles being greater than a predetermined cardiac cyclesthreshold.
 17. The method of claim 16, wherein the first patientcharacteristic comprises a patient age and further comprising:performing the first update of the virtual lead days value in responseto the patient age being within a predetermined patient age range; andnot performing the first update of the virtual lead days value inresponse to the patient age being outside the predetermined patient agerange.
 18. The method of claim 12, further comprising: comparing theupdated virtual lead days to a plurality of predetermined thresholds;and increasing the frequency of determining whether the lead conditionid occurring in response to the comparing.
 19. The method of claim 12,wherein the first patient characteristic comprises a patient age andfurther comprising: performing the first update of the virtual lead daysvalue in response to the patient age being within a predeterminedpatient age range; and not performing the first update of the virtuallead days value in response to the patient age being outside thepredetermined patient age range.
 20. The method of claim 19, whereinsecond patient characteristic comprises a patient activity level and anumber of cardiac cycles, and further comprising determining the patientcharacteristic update is satisfied in response to one or both thepatient activity level being greater than a predetermined patientactivity level threshold and the number of cardiac cycles being greaterthan a predetermined cardiac cycles threshold.
 21. The method of claim12, wherein the processor is configured to compare the updated virtuallead days to a plurality of predetermined thresholds, and increase thefrequency of determining whether the lead condition id occurring inresponse to the comparing.
 22. The method of claim 12, furthercomprising: determining one or more impedance values in response to thedelivered therapy a predetermined number of times during a predeterminedtime period; determining whether the lead condition is occurring inresponse to the determined one or more impedance values; and updatingthe frequency of determining whether the lead condition is occurring inresponse to the increased predetermined number of times.
 23. Anon-transitory computer readable medium storing a set of instructionswhich when implemented in a medical device cause the device to perform amethod for updating a frequency of determining whether a lead conditionis occurring, the method comprising: sensing a cardiac signal;determining whether a lead condition is occurring in response to thesensed cardiac signal; determining whether a first patientcharacteristic is satisfied during a plurality of predetermined updateperiods; performing a first update of a virtual lead days valueassociated with a number of days since implant of the lead in responseto the first patient characteristic being satisfied; determining whethera patient characteristic update is satisfied in response to a secondpatient characteristic, different than the first patient characteristic,being satisfied; performing a second update of the virtual lead daysvalue in response to the patient characteristic update being satisfied;and updating a frequency of determining whether the lead condition isoccurring in response to the updated virtual lead days value.